Case of the Week
Section Editors: Matylda Machnowska1 and Anvita Pauranik2
1University of Toronto, Toronto, Ontario, Canada
2BC Children's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
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August 31, 2015
Myotonic Dystrophy Type 1
- Background:
- Myotonic dystrophy type 1 (DM1) is an autosomal-dominant multisystem disorder associated with an unstable triplet repeat of the DMPK gene. Two subtypes exist: 1) DM1, also called Steinert disease, has a severe congenital form and an adult-onset form, and 2) myotonic dystrophy type 2 (DM2), also called proximal myotonic myopathy (PROMM), is rarer than DM1 and generally manifests with milder signs and symptoms.
- Clinical Presentation:
- Variable, progressive disability; facial and distal limb muscle weakness with myotonia; cataracts; cardiac conduction defects; diabetes mellitus; and, in males, testicular atrophy
- Key Diagnostic Features:
- MRI features: Subcortical hyperintensity of the white matter on T2-weighted sequences, with a predilection for the anterior temporal lobes. Typically, sparing of the basal ganglia, thalamus, and brainstem. The presence of prominent perivascular spaces and cerebral atrophy are also characteristic.
- Bilateral temporal lobe hyperintensity can be seen in several disorders. The confluent white matter lesions in the anterior temporal lobes of DM1 can be confused with CADASIL (cerebral autosomal-dominant arteriopathy with subcortical infarts and leukoencephalopathy). However, in CADASIL there is often the presence of lacunar infarcts affecting the external capsule, insular cortex, and basal ganglia, as well as a history of headache, stroke-like symptoms, and dementia.
- In contrast to other conditions, in DM1 there are often associated calvarial abnormalities with thickening of the skull due to a generalized hyperostotic potential. Prominence of the frontal sinus, craniokyphosis (small basal angle), and ossification of the falx cerebri are other described features.
- DDx:
- CADASIL
- Gliomatosis cerebri
- Herpes simplex viral encephalitis
- MELAS (mitochondiral encephalopathy, lactic acidosis, and stroke-like episode)
- Rx: Currently no cure or treatment. Symptomatic treatment to prevent heart arrhythmias and myotonia.
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